The 30-day rule: buy it back and the cost changes
Sell 10,000 units for £50,000 and buy back on day ten and the allowable loss is £2,000, not £30,000 — £28,000 deferred into the pool. It catches gains too.
Tax mechanic · 14 Sep 2026HMRC rules · 2026/27
2026/27 tax year. General information, not tax advice — your circumstances decide the treatment.
| Annual exempt amount | £3,000 |
| Basic rate taxpayers | 18% |
| Higher & additional rate | 24% |
| Report even if under the allowance | if proceeds exceed £50,000 |
More than most people expect. Selling for pounds is obvious, but swapping one coin for another is a disposal of the first, spending crypto on goods is a disposal, and so is gifting to anyone other than a spouse or civil partner. Moving coins between your own wallets is not.
The allowance fell from £12,300 in 2022/23 to £6,000, then to £3,000 — so gains that were comfortably covered three years ago now generate a bill.
Coins you mine are income at the moment you receive them, valued in pounds on that day, taxed at 20%, 40% or 45% depending on your band. That value then becomes your cost basis. When you later sell, any further gain is a separate capital gains event.
Whether HMRC treats mining as trading income or miscellaneous income depends on scale, organisation and commerciality — a rig in the spare room is usually the latter. It matters, because trading treatment allows expenses like electricity to be deducted more generously.
HMRC applies three rules in strict order. Same-day: disposals match acquisitions on the same day first. Then the 30-day “bed and breakfast” rule, matching against anything bought in the following 30 days. Anything left falls into the Section 104 pool, an average cost across all remaining holdings of that asset.
This is what makes manual crypto accounting painful, and why most people with more than a handful of transactions end up using dedicated software.
The Cryptoasset Reporting Framework took effect on 1 January 2026. UK platforms must collect and report user identity and transaction data to HMRC automatically, with international exchange of the same data between jurisdictions. Previously HMRC had to request information case by case.
You are also now required to give accurate personal details to platforms you use. Getting that wrong can attract a penalty of up to £300, and more from non-UK providers.
Gains go on the SA108 capital gains pages alongside your SA100; crypto income goes in the income section of the return. Online filing deadline is 31 January following the end of the tax year; paper returns are due 31 October.
Losses are worth recording even in years you owe nothing — once reported they carry forward indefinitely against future gains.
2026/27 rates. Everything stays in your browser — nothing is sent anywhere.
Capital gains do not have their own separate rate. They stack on top of your taxable income, and only the room left inside the basic rate band is charged at 18% — everything above it at 24%. A £20,000 gain costs £3,060 on a £30,000 salary and £4,080 on a £70,000 one. Same gain, a third more tax.
This is also why the £100,000 income mark hurts so much. The personal allowance tapers away above it, so mining income landing in that zone can be taxed at an effective 60%.
It will not work out your gain for you. That needs HMRC's matching rules applied in order — same-day first, then the 30-day rule, then Section 104 pooling — across every disposal you made. With more than a handful of transactions that is a job for dedicated software or an accountant, and the number it produces is what you type into the box above.
It also assumes English, Welsh or Northern Irish income tax bands. Scotland sets its own rates on earned income, which changes the income tax figure but not the CGT rates — those are UK-wide.
Sell 10,000 units for £50,000 and buy back on day ten and the allowable loss is £2,000, not £30,000 — £28,000 deferred into the pool. It catches gains too.
Tax mechanic · 14 Sep 2026Never registering for Self Assessment makes it a failure to notify, and the window is 20 years whatever your state of mind. On £10,000 of 2022/23 tax, interest alone is £2,036.99.
Situation · 14 Sep 2026HMRC lists seven items at CRYPTO10400 and asks you to keep them for 22 months, against an assessing window of up to 20 years. One lost 2017 receipt is £4,160 of extra tax.
Rules and reporting · 14 Sep 2026Buy and sell on one day and HMRC matches them against each other. On the worked example that is £324 of tax against £1,061.95 if the purchase is wrongly pooled.
Tax mechanic · 7 Sep 2026Mining receipts are income on the day they land, and that same value becomes the cost you deduct when you sell. Ignore the first step and you overstate the gain.
Situation · 7 Sep 2026Applications open 30 September and the regime commences 25 October 2027. Authorisation brings the Consumer Duty and the Ombudsman, and no compensation scheme.
Rules and reporting · 7 Sep 2026A pool of six units at £15,200 averages £2,533.33 each. Selling 2.5 units for £9,500 takes out £6,333.33 of cost and leaves a £3,166.67 gain — £166.67 of it taxable after the £3,000 allowance.
Tax mechanic · 31 Aug 2026HMRC sent 64,982 crypto nudge letters in 2024/25 and about 81,000 in 2025/26. On £4,000 of tax filed and paid a year late, penalties and interest add £3,310 to £3,710.
Situation · 31 Aug 2026Twelve round trips on £2,000 produce £27,361 of gross disposals reported to HMRC against a real gain of £536 — 51 times over, and entirely inside the £3,000 allowance.
Rules and reporting · 31 Aug 2026Sources: HMRC Cryptoassets Manual and current published rates. Figures change at each Budget. This is general information and not a substitute for an accountant.